1. Field of the Invention
The present invention relates in general to an integrated circuit manufacturing process. More particularly, the invention relates to an improved method for passivating aluminum connections to various semiconductor regions of an integrated circuit die.
2. Description Relative to the Prior Art
Aluminum contacts, which are deposited in openings of a silicon dioxide layer covering an underlying integrated circuit die, and aluminum metal runs, which are connected to respective contacts and are adherent to the top surface of the oxide layer, have been passivated in the prior art by a number of techniques. In one such technique, described in an article entitled "Application of Aluminum Oxide to Integrated Circuits Fabrication"; IEEE Transactions on Reliability; Volume R-25 No. 5; December 1976; semiconductor wafers were processed by a standard sequence of processing steps except that the wafers were also immersed in boiling deionized water after patterning of the aluminum metal runs. The heater water converts the exposed surface of the aluminum to aluminum oxide during this processing step. The aluminum oxide protects or passivates the aluminum which reduces the frequency of open circuit failures due to corrosion of the aluminum. After immersing the die in the boiling water, a standard thin film of passivating glass, such as phosphosilicate glass or borosilicate glass, is deposited over the oxidized aluminum runs and insulating layer covering the die to further protect the integrated circuit. The glass film and then the aluminum oxide were etched to expose wire bonding pads, e.g. ends of the aluminum runs normally located near edges of the die. The otherwise standard process was completed by wire bonding the contact pads to a lead frame and then encapsulating the die in an epoxy resin.
The glass film inevitably contains some defects such as pinholes, discontinuous coverage, or cracks. A disadvantage of this process is that when aluminum oxide is etched from the aluminum to expose the wire bonding pads, aluminum oxide exposed by defects in the glass may also be etched thereby exposing aluminum which otherwise should be passivated. Moisture can attack this aluminum as well as the exposed aluminum on the bonding pads. Also, ingredients contained in the epoxy resin may attack the bonding pads and the aluminum exposed by glass defects from which aluminum oxide has been etched. The moisture and/or resin can corrode the exposed aluminum to an extent that open circuit failures occur.